When did the new millennium begin?When did the 21st Century begin?, Astronomy Boy

If you ask these questions of 100 people, it's likely at least 90 of them will answer, "On January 1, 2000."

That sounds reasonable, but it's wrong. The new millennium, as defined by the Gregorian Calendar used in most of the world, actually began on January 1, 2001, not January 1, 2000. All of the "millennium" celebrations at the end of 1999 were one year too early! (Not that I object in any way to a good party!)

Why the Confusion?
Apparently, it's because it "sounds right" that a millennium (or a century) should begin with a nice, round number like 2000. This is sometimes called the "odometer effect" because many automobile owners perceive the rollover of their mileage indicators to include a long string of zeroes as a milestone of sorts.

Another contributor to the misunderstanding was the Y2K computer bug that affected many computer systems at the start of the year 2000. This very real problem was erroneously called the "millennium bug" during much of the reporting on the subject.

Both of these factors made it seem plausible that the new millennium began in 2000. However, a quick look into the history of our calendar shows us that is incorrect.

Some History
Our current calendar system may rightly be considered a historical accident. Like so much of history, it is not necessarily logical or convenient. If you must blame someone for the millennium confusion, blame the ancient Romans.

Around the year 525, the Roman monk Dionysius Exiguus was working out a list of the dates of Easter. In the course of his work, he also reckoned the birth year of Christ, and designated it as 1 AD.

As Dionysius counted them, the years surrounding the birth of Christ were:

3 BC 2 BC 1 BC 1 AD(Christ's birth)2 AD 3 AD etc.

Why did Dionysius leave out the Year Zero? That's an easy one. The counting system used in 6th century Rome did not include the concept of "zero." The idea of "zero" was unknown to Dionysius. (If you recall the Roman numerals you learned in school, you'll remember there was no symbol for Zero.)

So, in designating the birth year of Christ as 1 AD, Dionysius chose the only starting point he knew: the Year One. This is critical to understanding when the next millennium begins.

Now, jump ahead more than 1000 years. In 1582, Pope Gregory XIII ordered that the Julian Calendar then in common use be reformed. The Gregorian Calendar Reform, as it came to be called, retained Dionysius' starting point of 1 AD and his system of counting the years, including its lack of a Year Zero. With the powerful influence of the Roman Catholic Church behind it, the Gregorian Calendar  with its starting point of 1 AD  was gradually adopted throughout the world.

You can argue that it's not logical. You can argue that Dionysius probably got the year of Christ's birth wrong. You can even find special-purpose calendar systems that do include a Year Zero.

In deciding when the new century or millennium began, none of this matters.

What matters is that the calendar we use today  the Gregorian Calendar  starts with the year 1 AD and has no Year Zero. For better or worse, we're stuck with it! (For a further discussion of the Year Zero problem, see Millennium Mistake, by Jan Zuidhoek.)

[Please note: I am fully aware that many other calendar systems exist. When I speak of the Gregorian calendar as "the calendar we use today," I am referring to the fact that the Gregorian Calendar is the most commonly used civil calendar. Many cultures also utilize other calendars, primarily religious ones, but the Gregorian Calendar is the closest thing to an "official" or "universal" calendar for most of the world.]

So, When Do Centuries Begin?
Because of Dionysius and Pope Gregory, centuries always start with a year ending in 1 (one). Why? Because the very first century of the Gregorian calendar began with the Year 1 AD, and everything else has to follow from that:

Century

Years (AD)

Century

Years (AD)

1st Century

1 - 100

12th Century

1101 - 1200

2nd Century

101 - 200

13th Century

1201 - 1300

3rd Century

201 - 300

14th Century

1301 - 1400

4th Century

301 - 400

15th Century

1401 - 1500

5th Century

401 - 500

16th Century

1501 - 1600

6th Century

501 - 600

17th Century

1601 - 1700

7th Century

601 - 700

18th Century

1701 - 1800

8th Century

701 - 800

19th Century

1801 - 1900

9th Century

801 - 900

20th Century

1901 - 2000

10th Century

901 - 1000

21st Century

2001 - 2100

11th Century

1001 - 1100

22nd Century

2101 - 2200

So every century begins with a year ending in 1 (one) and concludes with a year ending in 0 (zero). The 21st Century is no exception; it began in 2001, not 2000.

What About Millennia?
The millennium works exactly the same way as the century. Each millennium begins with a year ending in 1 (one) and concludes with a year ending in 0 (zero):

Millennium

Years (AD)

First Millennium

1-1000

Second Millennium

1001-2000

Third Millennium

2001-3000

The new millennium began on January 1, 2001, on the same day that the 21st Century began.

Why should YOU care?
I'm glad you asked. This sort of mistake is a symptom of the "dumbing down" of society. The mistake itself is understandable. What's alarming is that when you point out the mistake, many (most?) people can't bring themselves to think about it, preferring "intentional ignorance" instead. And if you are knowledgeable about the subject, people think you are either very odd or some sort of genius!

Even worse is the effect this sort of ignorance has on children. Today's kids are growing up in a world where ignorance is blissfully tolerated. Too many people have come to believe that everything  even a historical fact  is a matter of opinion. When children embrace the idea that something is true if enough people believe it, the incentive to pursue critical thinking, education, and hard work begins to disappear.

What should YOU do?First of all, I hope you had a wonderful time at all the "millennium" parties at the end of 1999 and at the "real millennium" parties at the end of 2000! Even though the reasons for the 1999 celebrations were wrong, that's no excuse for missing a good time.

Don't be afraid to explain the facts, especially to children. Kids are often willing to accept ideas that adults refuse to think about. Don't ever be embarrassed because you know how to count.

Grab the banner below, and put it on your website. Link it to this page. If it helps even a few people think for themselves and learn something, it's worthwhile.